I've just started a little project with my brand new Arduino Mega 2560 and things seemed to work till today when i came back from work. I connected the board via USB to the pc, tried uploading a modified version of my last sketch and......i get a timeout on uploading. The bootloader seems to be fine cause when i reset the board, the led connected to pin 13 flash 2 times. I've tried to change USB port, change comupter, unistall and reinstall driver...nothing works. The UI send the first string to the board, and RX led flash shortly then it doesn't send anything...TX stay off. Here is some output from the command line (Shift pressed while clicking uploading).

I have similar problems and many other people do too- it seems an issue with the bootloader. I have searched and no one on the forum can give a straight answer how to re burn the 2560 bootloader. there are 100 half answers. i found the developer who actually programed the bootloader and sent him an email a few hours ago for a step by step guide specifically for the 2560. I hope to have a difinitive answer soon!

I thinked it's a bootloader problem too, but it seems it's booting ok because it flash 2 times after a reset. However we can try flash it with a parallel cable http://arduino.cc/en/Hacking/ParallelProgrammer .

If the developer reply to you please write here =) i'm still searching a soliution!

no response from the developer yet- but I talked to spark fun where is bought it and sent them my tests... I did the "general test" and the "tone test" direct from the Arduino IDE version 22... both with failed results. Sparkfun said it was the bootloader too and has a tutorial to re-burn here:http://www.sparkfun.com/tutorials/247

the tutorial is for an UNO, so the only change you need to make is in the FUSE file with this:#############################################mega2560.name=Arduino Mega 2560

The only problem is that we need a programmer or another arduino (wich i don't have). Since i bought my arduino in MY electronic store i think it's faster to send in RMA the old arduino and get a new one! xD

I just completed my RMA too, I hope the new board is solid. Good Luck on your Projects!

OH YES- I heard back from the the Bootloader Developer. He said don't put !!! anywhere in your code. There is a bug when you use 3 exclamations in a row, no matter how you use them, the bootloader tries to go to a monitor mode and breaks the sketch. no !!!